1. Field of the Invention
The present invention generally relates to measurement method and apparatus for measuring characteristics of a radio-wave, in particular, to a measurement technique for measuring a desired-signal power, an interference-signal power, and/or an SIR (signal-to-interference power ratio) in, for example, a diversity combining receiver/transceiver.
2. Description of the Related Art
A prior art of the SIR measuring method is disclosed by the following article:
xe2x80x9cAn Investigation on SIR Measurement Methods in Adaptive Transmit Power Control for DS-CDMAxe2x80x9d by S. Seo, Y. Okumura and T. Dohi, Proc. Communications Society, The Institute of Electronics, Information and Communication Engineers (IEICE), B-330, pp. 331, 1996.
The above article describes an SIR measurement method. In the method, a desired-signal power is obtained from a square of an average value of the envelope of a received signal resulted from the diversity reception within a predetermined symbol-period, while an interference-signal power is obtained as a variance of the average value of the envelope of the diversity reception signal within a predetermined symbol-period. Then, SIR is calculated by obtaining a ratio between these signal powers. However, the method needs complicated calculation to obtain the desired-signal power and the interference-signal power. Since, furthermore, the desired-signal power is estimated as an averaged value of the received signal, the power cannot be measured with high accuracy. A problem in this method will be briefly described below.
A signal r1 received at a receiver channel 1 and a signal r2 received at a receiver channel 2 can be written as:
r1=s1+i1xe2x80x83xe2x80x83(1)
r2=s2+i2xe2x80x83xe2x80x83(2)
where s1, s2 and i1, i2 respectively represent the values of the desired-signal amplitude and the interference-signal amplitude contained in the received signals r1 and r2.
Combining r1 and r2, using a maximal-ratio combining method, gives:
s1(s1+i1)+s2(s2+i2)=s1{circumflex over ( )}2+s2{circumflex over ( )}2+s1*i1+s2*i2.xe2x80x83xe2x80x83(3)
where xe2x80x9c{circumflex over ( )}2xe2x80x9d denotes a square.
Now assume that i1{circumflex over ( )}2=i2{circumflex over ( )}2=N0 and the average values of i1 and i2 are equal to zero. The desired-signal power Sxe2x80x2 and the interference-signal power Ixe2x80x2 appearing in the article cited above are then given by the expressions:
Sxe2x80x2=(s1{circumflex over ( )}2+s2{circumflex over ( )}2){circumflex over ( )}2xe2x80x83xe2x80x83(4)
Ixe2x80x2=(s1{circumflex over ( )}2+s2{circumflex over ( )}2)*N0xe2x80x83xe2x80x83(5)
Hence, the signal-to-interference power ratio (SIR) can be written as:
Sxe2x80x2/Ixe2x80x2=(s1{circumflex over ( )}2+s2{circumflex over ( )}2)/N0xe2x80x83xe2x80x83(6)
However, Sxe2x80x2 and Ixe2x80x2 calculated above do not represent the respective actual or real values of the desired-signal power and the interference-signal power. The following calculation must be therefore performed in order to obtain the actual values:
S=sqrt(Sxe2x80x2)xe2x80x83xe2x80x83(7)
I=Ixe2x80x2/sqrt(Sxe2x80x2)xe2x80x83xe2x80x83(8)
where xe2x80x9csqrtxe2x80x9d denotes a square root.
Thus, this method requires complicated calculations to arrive at the actual values S and I for the desired-signal power and the interference-signal power, respectively.
It should be also noted that an averaging treatment over a long symbol-period is employed for obtaining an interference-signal power with high accuracy in the method described in the above-mentioned article. Since, however, the interference-signal power Ixe2x80x2 in Eq.(8) contains a time-varying term (s1{circumflex over ( )}2+s2{circumflex over ( )}2), the accuracy of the measurement will be reduced even with the long-period averaging. In order to avoid such problem, the desired-signal power S and the interference-signal power I must be determined exactly. It follows that the method has a drawback of requiring complicated calculations as mentioned above.
It is an object of the present invention to provide method and apparatus for measuring radio-wave characteristics such as an SIR with high accuracy through a simple calculation process.
To achieve the above object, the present invention provides, in a first aspect, a method for measuring characteristics of a propagated radio-wave on the basis of a reference signal, wherein the reference signal is obtained by receiving and demodulating the propagated radio-wave. The method comprises the steps of: (1) within a signal-processing channel, estimating characteristics of a propagation-path through which the radio wave has transmitted, on the basis of the reference signal, and (2) determining radio-wave characteristics on the basis of the estimated characteristics.
The present invention further provides, in a second aspect, a method comprising the steps of: (1) within a signal-processing channel, estimating characteristics of a propagation-path through which the radio wave has transmitted, on the basis of the reference signal, (2) determining a first radio-wave characteristic on the basis of the estimated characteristics, and (3) within the respective signal-processing channels, calculating a difference value between the estimated characteristics and the reference signal so as to obtain a second radio-wave characteristic.
The present invention also provides, in a third aspect, a method further comprising the step of deriving a third radio-wave characteristic from the radio-wave characteristics calculated in the respective signal-processing channels.
In a further aspect, the present invention provides either a receiver or a transceiver that performs either one of the foregoing methods.